1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus each having the electrophotographic photosensitive member.
2. Description of the Related Art
An organic electrophotographic photosensitive member having a support and a photosensitive layer (organic photosensitive layer) provided thereon using an organic material as a photoconductive substance (a charge generating substance or a charge transporting substance) has been in widespread use as an electrophotographic photosensitive member because of its advantages, that is, a low cost and high productivity. An electrophotographic photosensitive member having a lamination type photosensitive layer with a charge generating layer containing a charge generating substance and a charge transporting layer containing a charge transporting substance superposed one on the other has been the mainstream of the organic electrophotographic photosensitive member because of its advantages such as high sensitivity and a possibility of designing various materials. Examples of the charge generating substance include a photoconductive dye and a photoconductive pigment, and examples of the charge transporting substance include a photoconductive polymer and a photoconductive low-molecular-weight compound.
Since electrical external force or/and mechanical external force is/are directly applied to the surface of an electrophotographic photosensitive member during charging, exposure, development, transfer or cleaning, a large number of problems caused by those external forces occur on the surface. Specific examples of the problems include: deterioration in durability and transfer efficiency of the electrophotographic photosensitive member due to flaws on a surface layer of the electrophotographic photosensitive member or generation of wear; melt adhesion of toner; and image defects due to cleaning failure.
To deal with those problems, active investigation has been conducted to improve a surface layer in an electrophotographic photosensitive member. To be specific, investigation has been made into the improvement of a resin from which the surface layer is formed and into the addition of filler or water repellent material from the aspect of material for the purposes of increasing the strength of the surface layer and of imparting high releasability or lubricity to the surface layer.
Meanwhile, as an improvement from the aspect of physical properties, investigation has been made also to solve the above-mentioned problems by suitably roughening the surface layer. Since the roughening of the surface layer can reduce a contact area at which a toner, a charging member, a transferring member or a cleaning member is brought into contact with the surface layer, it is expected to exert an effect of improving releasability or an effect of reducing frictional force. The frictional force between the surface layer and a cleaning blade is particularly large, which is liable to raise a problem of deterioration in cleaning performance or in durability. Specific examples of the problems resulting from deterioration in cleaning performance include cleaning failure due to: chattering or turn-up of a cleaning blade; and gouging or chipping of a blade edge. Herein, the chattering of a cleaning blade is a phenomenon in which the cleaning blade vibrates owing to an increase in frictional resistance between the cleaning blade and the surface of an electrophotographic photosensitive member. In addition, the turn-up of a cleaning blade is a phenomenon in which the cleaning blade turns up in the direction in which the electrophotographic photosensitive member moves. Specific examples of the problems resulting from deterioration in durability include an increase in the amount of wear of the surface layer attributable to an increase in frictional resistance and the generation of flaws due to locally concentrated pressure. The above-mentioned roughening is expected to act advantageously on those problems.
An influence of toner (toner particles and an external additive) on both an electrophotographic photosensitive member and a cleaning member must be taken into consideration for expressing cleaning performance.
In general, good cleaning performance is considered to be expressed in the state that toner remaining on the surface of the photosensitive member without being transferred intervenes between a cleaning blade and the surface of an electrophotographic photosensitive member and reduces the frictional resistance generated between the two. However, in some electrophotographic processes, the amount of the above-mentioned toner intervening between the cleaning blade and the surface of the electrophotographic photosensitive member may be extremely small. For example, when a large number of patterns having low printing density are printed, or when monochrome images are continuously printed in an electrophotographic system according to a tandem mode, the frictional resistance between a cleaning blade and the surface of an electrophotographic photosensitive member is considered to be apt to increase particularly remarkably, and so the above-mentioned problem of deterioration in cleaning performance or in durability tends to be generated. Further, a problem concerning melt adhesion of toner resulting from an increase in frictional resistance may occur.
Those problems occurring between a cleaning blade and an electrophotographic photosensitive member generally tend to be remarkable as the mechanical strength of the surface layer of the electrophotographic photosensitive member increases and the peripheral surface of the electrophotographic photosensitive member is more difficult to abrade. Accordingly, the roughening of the surface layer is expected to be a very effective measure for alleviating a detrimental effect of such an increase in strength of the surface layer by the improvement of the resin of the surface layer as described above.
Examples of a technique of roughening the surface layer of an electrophotographic photosensitive member include:
a technique of controlling the surface roughness (roughness of the peripheral surface) of the electrophotographic photosensitive member within a specific range for facilitating the separation of a transfer material from the surface of the electrophotographic photosensitive member and a method of roughening the surface of the electrophotographic photosensitive member in an orange peel state by controlling drying conditions for forming the surface layer (Japanese Patent Application Laid-Open No. S53-92133);
a technique of roughening the surface of the electrophotographic photosensitive member by incorporating particles into the surface layer (Japanese Patent Application Laid-Open No. S52-26226);
a technique of roughening the surface of the electrophotographic photosensitive member by polishing the surface of the surface layer with a metallic wire brush (Japanese Patent Application Laid-Open No. S57-94772);
a technique of roughening the surface of an organic electrophotographic photosensitive member for solving the turn-up of a cleaning blade and the chipping of the edge portion of a blade, which become problems when the photosensitive member is used in an electrophotographic apparatus using a specific cleaning device and specific toner, and having a specific process speed or higher (Japanese Patent Application Laid-Open No. H01-099060);
a technique of roughening the surface of the electrophotographic photosensitive member by polishing the surface of the surface layer with a filmy abrasive (Japanese Patent Application Laid-Open No. H02-139566); and
a technique of roughening the peripheral surface of the electrophotographic photosensitive member by blasting (Japanese Patent Application Laid-Open No. H02-150850).
However, details of the surface profile of the electrophotographic photosensitive member roughened as described above are not specifically described.
The roughening of surfaces according to the prior art exerts a certain effect of reducing the above-mentioned frictional force between a surface layer and a cleaning blade because the surface layer is moderately roughened, but an additional improvement is being sought. In the respect that the surface profile of the surface layer is streaky or is in indefinite form or has unevenness with a difference in size, an additional improvement is being sought in order to solve problems on how to control cleaning performance and prevent a developer or paper powder from adhering, from a microscopic viewpoint.
An electrophotographic photosensitive member having a predetermined dimple shape has been proposed as a result of detailed analysis and investigation focusing attention to the control of the surface profile of an electrophotographic photosensitive member (WO 2005/093518 A). This proposal has hit a directionality to solve problems concerning cleaning performance and rubbing memory, but an additional improvement in performance of the electrophotographic photosensitive member is being sought.
In addition, a technique of subjecting the surface of an electrophotographic photosensitive member to compression forming with a stamper having unevenness in the form of wells has been disclosed (Japanese Patent Application Laid-Open No. 2001-066814). This technique is expected to be more effective in solving the above-mentioned problems because it enables an unevenness profile with independent shapes to be formed on the surface of an electrophotographic photosensitive member with higher controllability than the techniques disclosed in the above patent documents. According to this technique, it has been reported that an unevenness profile in the form of wells each having a length or pitch of 10 to 3,000 nm is formed on the surface of an electrophotographic photosensitive member, and releasability of toner is improved and nip pressure for a cleaning blade can be reduced, whereby the wear of the photosensitive member can be reduced. However, a photosensitive member having such an unevenness profile tends to cause image defects resulting from cleaning failure under a low-temperature, low-humidity environment. In addition, a problem of image defects due to melt adhesion of toner starting from depressed portions in the form of wells having a length of 10 to 3,000 nm as described above is liable to occur. This phenomenon tends to be particularly remarkable in a high-temperature, high-humidity environment where the adhesive force or frictional force between the surface of an electrophotographic photosensitive member and toner or a member coming in contact with the surface is apt to be large.
As described above, the prior art exerts a certain effect of improving the durability or cleaning performance of an electrophotographic photosensitive member and a certain effect of suppressing image defects, but is now still susceptible to improvement in order that the overall performance of an electrophotographic photosensitive member is further improved.
Therefore, it is necessary to develop an electrophotographic photosensitive member exerting good cleaning performance and causing no image defects in various environments.